North American otter description

Like other otter species, the North American otter has a long, sinuous, streamlined body, highly modified for aquatic life (3)(5)(6). The limbs are short and powerful, the clawed paws are fully-webbed, and the flattish head terminates in a broad muzzle equipped with numerous sensitive whickers used for detecting prey underwater (2)(3)(5). To propel itself through the water, this species primarily combines hind-limb paddling with vertical undulations of its remarkably long, tapering tail (3)(5)(7). The body is covered in densely packed underfur, overlaid with longer guard hairs that trap a layer of insulating air when the otter is swimming underwater (5). Generally the sleek outer fur is brown to velvety black above, and paler greyish-brown to silver underneath, but there is considerable regional variation in this species’ appearance, with numerous recognised subspecies(2)(6). Although the sexes are identical in overall appearance, the males are, on average, around five percent larger than the females (3).

Related species

North American otter biology

For most of the year, the North American otter is most active from dusk till dawn, but in the winter months, it may be more commonly seen during the day (2). Slow-moving fish, and to a lesser extent amphibians and crustaceans, are this species' favoured fare, but a wide range of other food types feature opportunistically in its diet, including birds, reptiles, molluscs, small mammals, and fruit (1)(2)(3)(7). A quick lunge from a position of ambush is the most commonly employed hunting method, but prolonged chases do sometimes occur (2). In the water, this otter has few natural predators aside from alligators, American crocodiles and killer whales, but on land it is much more vulnerable, with bobcats, cougars, coyotes, dogs and wolves all being potential threats (1)(2).

The social structure of the North American otter is extremely variable, with some animals being solitary, whilst others live in family units comprising an adult female with offspring, or occasionally even in large groups made up solely of adult males (2)(3). Groups of otters typically hunt and travel together, and will also utilise the same den and resting sites (2). Dens are made in riverside burrows, under rocks or vegetation near water, in hollow trees or undercut banks, or even in beaver and muskrat lodges (2)(6). There is considerable overlap in individual home ranges, and although this otter is non-territorial, scent-marking with faeces, urine and scent glands is an important form of communication (2)(7). Various vocalisations are also used to communicate, with the most common sound heard amongst a group of otters being a low frequency 'chuckling', while explosive snorts are often used to signal potential danger (2)(3).

Breeding takes place once a year around late winter and spring. Although the actual gestation period is only 60 to 63 days, there may be a period of delayed implantation for up to 8 months following copulation (2)(3)(7)(8). Up to five cubs are born at a time, with the female alone taking responsibility for parental care (2)(7). The young begin to play when around five to six weeks old, and are weaned at three to four months, but will normally remain with their mother for ten months or more (1)(2)(7). In captivity, North American otters may reach up to 25 years of age, but typically do not live longer than 13 years of age in the wild (1).

North American otter range

The North American otter occurs through much of Canada and the United States, from the Atlantic to the Pacific coast, and from the Gulf of Mexico up to northern Alaska (1)(3)(7). Following European settlement, it disappeared from large parts of its historical range, particularly in the interior of the United States, but reintroductions in recent years have seen this species’ distribution expand again (1)(3).

Species with a similar range

North American otter habitat

Owing to its aquatic nature, the North American otter is confined to areas with permanent water (3). However, this includes a wide variety of habitats from rivers, creeks and streams, to coastal waters, swamps and lakes (1)(2)(3).

North American otter status

North American otter threats

By the turn of the 20th century, the North American otter had been extirpated from large parts of its range as a result of habitat loss, pollution, and unregulated trapping for its luxuriant fur (1)(3)(8). In particular, the development of coal, oil, gas, tanning and timber industries had a devastating impact on the quality of wetlands and other water bodies throughout the continent (1). Fortunately, since then, the otter population has undergone a significant recovery, owing to reintroduction efforts, and improvements in trapping management and water quality (1)(2).

Today, the range of factors that threaten North American otter populations vary from region to region (1). In coastal areas, this species is extremely vulnerable to oil spills (1), with an untold number having died in the aftermath of the grounding of the Exxon Valdez off Alaska in 1989 (5). Chemical pollution is more of a problem inland, where the outflow of harmful pollutants into lakes and rivers can be extremely detrimental to the survivorship of this highly sensitive species (1)(3). In remnant areas where otters have been reintroduced, there is increasing discussion over the loss of intra-species diversity resulting from the mixing of different subspecies(1).

While otter trapping continues, with between 20,000 to 30,000 individuals taken annually for the fur trade (9), the current harvest strategies are not thought to pose a threat to the sustainability of existing populations (1). Nonetheless, there is concern that current harvest rates are limiting this species potential to expand its range in some areas (1)(2).

North American otter conservation

In order to control the fur trade, the North American otter is listed on Appendix II of CITES, which makes the international trade of any part of this species illegal without a permit (1)(4). Reintroduction projects have been critical to the re-establishment of otter populations in many parts of the United States, especially in the interior. However, owing to development and poor water quality, this species remains rare or absent in large parts of the south-western United States. Therefore, to make further strides in the recovery of the North American otter, additional research is needed to evaluate the impact the various forms of pollution and degradation are having on populations of this charismatic species (1)(2).

Authentication

Glossary

Amphibians

Cold-blooded vertebrates of the class Amphibia, such as frogs or salamanders, which characteristically hatch as aquatic larvae with gills. The larvae then transform into adults with air-breathing lungs

Crustaceans

Diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.

Gestation

The state of being pregnant; the period from conception to birth.

Molluscs

A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

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